ANIMAL HEAT. 305 



than venous, that is, requires more caloric to preserve it at 

 the same temperature, the heat becomes latent in saturating 

 this increased capacity of arterial blood ; and is gradually 

 given off in every part of the body, as the blood assumes the 

 venous character./ But unfortunately for this theory, it has 

 been ascertained that there is no difference, and that arterial 

 and venous blood have an equal capacity for heat. 



5. But however it may be explained, no one can doubt, 

 that calorification is closely connected with respiration. If 

 the latter is increased by any cause, the heat of the body is 

 also increased. When it is impeded, as in asthma, fainting, 

 breathing deleterious gases, and suffocationf the animal heat 

 is sensibly diminished J Those animals whose respiratory ap- 

 paratus is the most perfect and the best developed, have the 

 highest temperature, as we see in birds, whose bodies are sev- 

 eral degrees warmer than the human species. 



6. On the contrary, if we look at the cold-blooded ani- 

 mals, we shall find that a large proportion of them live in 

 water, where the supply of oxygen is but scanty, and that 

 their respiration is very imperfect); while in animals that 

 lie torpid during the winter, and are quite cold, respiration 

 is almost if not quite suspended. According to Majendie, 

 respiration produces (jour-fifths of the heat in herbivorous 

 animals ;){ three-fourths in carniverous, and the same in 

 birds.) 



7. It is found by experiment, that arterial blood is warmer 

 than venous. \The blood is found to acquire one degree of 

 heat in passing through the lungs, and as the whole mass 

 of the blood passes through the lungs twenty times an hour, 

 it follows, that the system receives from respiration twenty 

 degrees of heat in an hour, or two hundred and forty degrees 

 every twelve hours! Respiration, then, is one of the chief 

 sources of animal neat. 



8. Another theory in relation to animal heat is, that it is 

 produced by, or (depends on, nervous influence.! This is 



26* 



